W0052

The Impact of the Beam Stop on Data Collection Strategies at Synchrotron Beamlines. R.W. Alkire, Robert Schuessler and Frank J. Rotella, Biosciences Div., Argonne National Laboratory, Argonne, IL 60439 USA, and John Gonczy and Gerold Rosenbaum, Univ. of Georgia, Athens, GA 30602 USA.

Large-area CCD detectors at third-generation synchrotrons have become indispensable to protein crystallography. The primary role of the beam stop is to prevent direct beam from striking these very expensive detectors. However, the distance between the sample and beam stop can have a significant effect on diffraction data quality due to the scattering of x-rays by air. Using a small vertical profile beam stop, we report the potential effects of air scattering caused by changing the beam-stop-to-sample distance in experiments carried out at the Structural Biology Center’s insertion device beamline (19ID) at Argonne’s Advanced Photon Source. Based on these results, suggestions will be given on how to optimize the diffraction signal by minimizing background during data collection.

This work was supported by the U.S. Dept. of Energy, Office of Biological and Environmental Research, under Contract W-31-109-ENG-38.